This research is aimed at developing state-of-the-art deterministic/probabilistic modeling frameworks of the fate, transport, and transformation of chemicals released into ground and surface waters for Superfund sites and other sources. The assessment of the risk associated with the total exposure due to Superfund sites and other sources involves evaluation of the hazard (e.g.,potential effect) of the chemical sources and the probability of exposure of the target organisms to the chemicals. The principal aims of this research are to calculate the mean and the probability distribution of the dose of chemicals to humans and aquatic organisms from selected Superfund sites; and predict the change in human dose and aquatic organism body burden due to Superfund remedial action. These aims will be accomplished by compiling existing data on Superfund sites with emphasis of the model chemicals (nickel, chromium, benzene, chloroform, methylmercury, cadmium, and PCB congeners) used in the Biomedical and Ecological components. Contemporary understanding of volatilization, sorption, and microbial degradation processes, together with the kinetics of uptake and disposition of chemicals in fish, will be incorporated into the ground and surface water models. Calibration and verification of the models will be accomplished with site-specific data. Preliminary probability distributions of expected exposure will be provided to Assay and Ecological components for use in laboratory experiments. Model prediction will then be made of the effectiveness of environmental controls at Superfund sites to meet target risk levels.